Sliding doors and windows have come into wide usage in building construction in recent years. The use of air-conditioning and its high energy cost have made it increasingly important to keep doors and windows closed. In public buildings or in homes where children are present, it is difficult to enforce door and window closing rules.
Because of the stated need, several patents have disclosed various spring and gravity motors for automatically closing sliding windows and doors immediately after they have been opened. While some of these motors have been designed to close slowly and evenly, none of them have been able to cope with the situation in which a person forces the door closed at a rate in excess of the normal closing rate of the motor. Such forceful closing of the door has resulted in damage to the motor or malfunctioning of the entire mechanism.